WASHINGTON — Veterans Affairs Secretary Eric Shinseki vowed Thursday to make changes in the agency that serves nearly 6.5 million veterans but also defended the department's health care system as comparable with private medical providers.

Shinseki, a former Army general, told the Senate Committee on Veterans' Affairs that he is dedicated to serving those who sacrificed for their country and pained by reports of delayed care and falsified record-keeping within the Department of Veterans Affairs.

"Any adverse incident like this makes me mad as hell," Shinseki said. "But at the same time it also saddens me. ... It's important to me to assure the veterans, to regain their trust."

Some committee members quoted VA documents showing a historic pattern of fraudulent record-keeping and complained about a lack of transparency and accountability from his department.

Sen. Richard Burr, R-N.C., described a phone call that Robert Petzel, VA undersecretary for health, made to regional VA officials nationwide after the Phoenix VA director was placed on leave recently. Burr was told that Petzel told administrators that the removal was "political, and she's done nothing wrong."

"Why should this committee, or any veteran in America, believe that change is going to happen?" demanded Sen. Richard Burr, R-N.C.

Shinseki, in answer, vowed to make changes in the VA if investigations substantiate allegations of flawed care and wrongdoing.

Sen. Johnny Isakson, R-Ga., quoted from a previously undisclosed 2010 memo in which a VA administrator filled eight pages describing various methods used by agency health care officials to "game the system" by falsifying delays in medical care.

Petzel, who appeared before the senators with Shinseki, said he was aware of that memo and of ongoing problems involving some VA employees' attempts to manipulate data on patient access to enhance their job performances and bonuses.

"We have worked very hard, Senator Isakson, to root out these inappropriate scheduling practices, these abuses," Petzel said.

Shinseki and Petzel were asked repeatedly whether they had ever fired an employee for such fraudulent practices. Shinseki said 3,000 VA employees had been removed in 2013 — retired, transferred or terminated — for misconduct. He did not identify any fired for falsifying records on patient waits.

Sen. Patty Murray, D-Wash., was among those who upbraided Shinseki for failing to provide information that Congress requested and for failing to address "deep, system-wide problems" that have damaged the VA's credibility.

"The lack of transparency and the lack of accountability are inexcusable and cannot continue," she said.

Committee Chairman Bernie Sanders, I-Vt., anticipating the criticism, opened the meeting by stressing that the VA has defenders who regard it as a model provider of health care and by noting that any major medical agency will have unhappy patients — especially one handling 85 million appointments annually.

Sanders referred to a survey that showed roughly 95% of veterans are satisfied with their care, and a magazine article that reported hospital errors as the third leading cause of death in the nation.

"There is no question in my mind that VA Health Care has problems, serious problems," Sanders said. "But it is not the case that the rest of health care in America is wonderful."

In written testimony, Shinseki emphasized his personal dedication and that of the department to serving veterans.

"VA provides safe, effective health care, equal to or exceeding the industry standard in many areas," his statement said. "We care deeply about every veteran. ... We can and we must do better. VA takes any allegations about patient care or employee misconduct very seriously."

Sen. John McCain, R-Ariz., who is not a member of the committee, also spoke angrily of the allegations in his home state and of frustrations veterans have expressed for years.

"Decent care for our veterans is the most solemn obligation our nation incurs," McCain said. "No one should be treated this way in a country as great as ours ... We should all be ashamed ... To date, the Obama administration has failed to respond in any effective manner."

A White House official said Shinseki requested more help with the VA's internal review, leading Obama's chief of staff, Denis McDonough, to tap Rob Nabors, White House deputy chief of staff, for the assignment. Shinseki said he welcomed Nabors' help in making sure veterans receive high-caliber health care in a timely fashion.

Republicans already have said the probe should be independent, not led by someone they say is a White House insider.

Shinseki's testimony and exchanges with hostile senators came amid national controversy over assertions that 40 patients at the Phoenix VA Health Care System may have died awaiting care.

Those allegations prompted a VA Office of Inspector General investigation and spurred similar allegations from Department of Veterans Affairs employees in Texas, Colorado, Illinois, Georgia, Wyoming and New Mexico.

In the face of mounting criticism, Shinseki announced two weeks ago that every VA clinic in the country will undergo an audit of patient record-keeping procedures and practices.

Some members of Congress, as well as two of the nation's largest veteran advocacy groups, have called for Shinseki to resign or be fired.

At one point during Thursday's hearing, Sen. Dean Heller, R-Nev., asked Shinseki directly: "Can you explain to me, knowing all this information, why you should not resign?"

Shinseki responded that he was on a mission, already has made improvements to the VA, and "we're not done yet."

However, Shinseki told the Senate panel Thursday that he intends to remain in place.

Meanwhile, in Phoenix, a new interim director took over the VA Health Care System this week, replacing Director Sharon Helman, whom Shinseki placed on leave along with two other administrators.

VA officials in Arizona and Washington, have denied intentionally falsifying patient wait-time information but have acknowledged confusion and discrepancies that Government Accounting Office investigations have uncovered in the past few years.

The Phoenix VA Health Care System, which includes a hospital and at least a half-dozen satellite clinics, serves about 80,000 veterans.

Burr listed numerous inspector general, GAO and other investigators' reports identifying long delays in medical care and inaccurate or bogus record-keeping as major VA issues.

"VA leadership should have been aware the system was facing a national scheduling crisis," Burr said. "Why were the national audits and statements of concern for the VA only made this month?"

Murray said she has pressed the department for years to eliminate the fraudulent reporting of patient access data. In 2012, she said, an administrator told her the practice was so prevalent that each time a directive was put out to stop the practice, lower officials in the agency began tearing it apart to find loopholes.

"The standard practice of the VA seems to be to hide the truth in order to look good," Murray added. "That has got to change."

A groundswell of outrage, pain and frustration has emerged among veterans who have attended demonstrations and flooded members of Congress with complaints about flawed care, delayed appointments and other dysfunction in the VA health care system.

After the inspector general completes its Arizona investigation, leaders of the House and Senate committees on veterans' affairs have vowed to conduct hearings. However, Sanders decided in the face of mounting controversy to provide a forum Thursday for Shinseki and some organizations representing veterans organizations to speak about the issue.

Before the committee hearing, the Iraq and Afghanistan Veterans of America and Project on Government Oversight staged a joint press conference to announce a protection plan for VA whistle-blowers and to urge deeper investigations leading to solutions.

"Instead of leaders of the VA medical centers fixing problems with the system, they are choosing to fix the books," said Tom Tarantino, chief policy officer with the veterans groups.

During Thursday's Senate hearing, committee members cautioned against a rush to judgment on the Phoenix investigation but unilaterally agreed that the VA health care system is troubled and suffers from failures of transparency, accountability and leadership.

Sanders stressed that all medical treatment networks have problems and urged the VA to be regarded in the context of 6.5 million patients — 236,000 seen daily — at 150 VA medical centers and more than 1,700 points of care employing more than 300,000 people.

Shinseki said the VA has enrolled 1 million additional veterans in the past few years and said he also is reviewing whether the department has adequate resources.